In current cellular mobile broadband systems the achievable data rates are strongly dependent on the users' positions in the network.
In order for wireless networks operators to solve one of their biggest problems—how to get more signal strength where one needs or wants it most, the operators have started in the recent years to deploy their own or rely on end users to buy very small Base Stations, in order to meet the increasing demand for data traffic. This new type of cell sites, referred to hereinbelow as “small cells” or “metro cells”, used in conjunction with wireless cells of the traditional cellular networks (macro cells). Networks that include both macro cells and metrocells are referred to herein as heterogeneous networks (HetNets).
The term “small cells” as used herein and throughout the specification and claims encompass femtocells, picocells microcells and metrocells. Small-cell networks can also be realized by means of distributed radio technology consisting of centralized baseband units and remote radio heads. Beamforming technology (focusing a radio signal on a very specific area) can be utilized to further enhance or focus small cell coverage. A common factor in all these approaches to small cells is that they are centrally managed by mobile network operators.
Small cells provide a small radio footprint, which can range from 10 meters within urban and in-building locations to 2 km for a rural location.
According to the solution being adopted by the operators, the end-users may buy small devices that are personal cellular base stations. The device typically has an antenna to boost the available signal as well as an Internet connection. The device uses the end user Internet connection to connect to the service provider's network and to route the user's phone calls.
As will be appreciated by those skilled in the art, scenarios that entail an overlapping deployment, while using the same or adjacent frequency channels, between two (or more) cells of the same or different types (e.g. macro, metro etc.) are possible.
The problem yet to be solved is how to enable efficient simultaneous operation of both macro cells and small cells where the latter are located within area covered by the macro cell, while providing the same user experience across the whole cellular network (or even better) in order to satisfy the users' expectations, and at the same time, while the macro cell can be unaware of small cells being operative within its range.
One of the problems associated with such a deployment is that along with the expected densification of small cells' deployments, there is a rapid increase in the number of physical layer identifiers (“PLI”s) that are used in modern cellular technologies to identify the Base Station for mobile terminals. Examples of such identifiers are PCI in LTE compatible systems and primary scrambling codes (“PSC”s) in UMTS compatible networks, or any other applicable physical layer identifiers in systems that are compatible with other International Standards. However, as the number of possible PLIs is limited, the probability of having PLI collision within the small cell grid, as well as between the small cells and the macro network, increases significantly. A large number of small cells effectively preclude the network operator from being able to manually assign PLIs to the various small cells. Therefore, the present invention seeks to provide a solution by which the PLIs may be allocated automatically and reassessed periodically in order to avoid PLI collisions at times when changes in network conditions occur.